Can a member of the European Parliament be removed from office before end of term? If so, on what grounds and who has the power to do it?
This has come up in casual conversation and my (cursory, I admit) research did not yield an answer.
It's quite complicated because the rules in this and in many other respects are the same than those that apply to the respective national parliament so that they differ depending on where the MEP in question was elected. Member states can therefore set their own rules “for the withdrawal of the mandate of a member of the European Parliament” (similarly, until 2009, MEP would get the same salary than national MP, which resulted in huge gaps between MEP from different countries).
One situation in which it could happen is when a MEP is found guilty of a crime. For that to happen, the authorities of the country where the procedure takes place first have to ask the parliament to drop the MEP immunity. And the extent of the parliamentary immunity also depends on the rules of the national parliament, so again might differ from one MEP to the next! You can find a brief Q&A on this on the website of the parliament.
The office of member of the European parliament is also incompatible with a number of other functions, including being a member of a national government. Should this happen, the member state of the MEP in question has to notify the president of the parliament so here again national rules and procedures apply.
Legally, the main source for all this is called “Act concerning the election of the Members of the European Parliament by direct universal suffrage (20 September 1976)” or simply “Act of 20 September 1976”. But as I explained it does not harmonize the rules and refers to “national provisions” in several places.